Neurodegenerative diseases such as Huntington's disease, amyotrophic lateral sclerosis or Parkinson's disease share one common feature, the slow accumulation of misfolded proteins. As misfolded proteins accumulate in neurons they are not evenly distributed. Instead, they are concentrated in inclusion bodies. How these inclusion bodies are linked to the progression of neurodegenerative diseases is not well understood. One class of inclusion bodies, aggresomes, are formed at the microtubule organizing center in an active process that requires microtubule-based transport. We recently discovered that the active concentration of misfolded proteins in aggresomes involves the Hook2 protein. Hook proteins constitute a family of coiled-coil proteins which bind to microtubules and affect the organization of different organelles in mammalian cells and in Drosophila. In this grant, we will combine genetic approaches in Drosophila, cell biological approaches in mammalian tissue culture cells and biochemical experiments in-vitro to characterize shared functions of Hook proteins, as well as the specific role of Hook2 in the cellular trafficking of misfolded proteins. In Spec. Aim 1, we will determine the relevance of microtubule binding of Hook proteins using a combination of biochemical approaches in vitro and genetic experiments in Drosophila. In this context we will also explore the potential interaction of Hook proteins with the complex between cytoplasmic Dynein and Dynactin. In Spec. Aim 2, we will characterize the binding of Hook proteins to different organelles and identify the receptors that mediate these interactions. In Spec. Aim 3, we will determine the role of Hook2 in the formation of aggresomes and the potential of using dominant-negative forms of Hook2 to manipulate the aggregation of different misfolded proteins. In Spec. Aim 4, we will determine the domains of Hook proteins responsible for their polarized distribution in neurons and the role of Hook proteins in establishing neuronal polarity in rat hippocampal neurons.